The possibility of biological machining by bacteria as a new technique for metal removal is investigated in this study. There are some kinds of chemolithotrophic bacteria, that gain energy from inorganic matter and fix carbon dioxide in the air. Among them, there is a particular bacteria, Thiobacillus ferrooxidans, which "eats" metals. Machining of grooves on pure iron and pure copper by Thiobacillus ferrooxidans is experimentally investigated. The experimental analysis made it clear that bio-machining was essentially possible, since the depth of the groove generated on the workpiece increased approximately proportionally to the machining time. Furthermore, electrolytic bio-machining proved to be even more effective, because the removal rate became much higher under an electric field.